Acoustical performance of a wavy micro-perforated panel absorber

In this study, the sound absorption performance of a wavy micro-perforated panel absorber (WMPPA) is investigated. First, a numerical model is established to calculate the sound absorption coefficients of micro-perforated panel absorbers (MPPAs) under normal, oblique, and random incidences. Subsequently, the proposed model is validated using an existing theoretical formula. After that, the acoustical properties of a WMPPA are explored and then compared with those of flat and corrugated micro-perforated panel absorbers (FMPPAs, CMPPAs). It is observed that the normal sound absorption curve of the WMPPA shifts to a lower frequency range compared with those of CMPPA and FMPPA, which is promising for the control of low-frequency noise. Besides, the sound absorption performance of the WMPPA at the dips is considerably improved, which is favourable for the reduction of broadband noise. Modal analysis shows that, apart from the resonant mode, the adjacent non-resonating modes are also excited, which enhances the performance. Moreover, the WMPPA exhibits the properties of a multiple-layered MPPA, and extra sound absorption peaks are observed within the middle- to high-frequency range. In addition, a parametric study is conducted to explore the influence of the corrugation depth and offset distance on the sound absorption performance of the WMPPA. The calculated results demonstrate that the proposed WMPPA is suitable for low-frequency and broadband noise control. Furthermore, a compact WMPPA with a high random sound absorption coefficient is obtained following an optimization scheme. Finally, the sound absorption coefficients of the MPPAs under normal plane-wave incidence are obtained experimentally using an impedance tube. The measurement results agree well with the simulation results, validating the proposed model and verifying some of the numerical findings.